In the process chain of die forging, an intermediate shape in relation to the final shape of the forged part is required. The result of the subsequent die forging is thus to be improved by an accumulation or reduction in mass at certain points of the workpiece. In order to obtain the intermediate shape, methods such as transverse rolling or stretch rolling, for example, are known.
Further methods are described in “Lehrbuch der Umformtechnik” [textbook of forming technology], Kurt Lange, Springer-Verlag 1974, page 46.
Both transverse rolling and stretch rolling permit optimum geometric adaptation of the mass distribution on the intermediately shaped part to the requirements for the die forging of elongated parts. The excess material in the final shape is thereby minimized and uniformly distributed and permits low-flash die forging. Due to the adaptation of the rolled intermediate shape to the final shape of the finish-forged part, constant forming forces and thus minimum tolerances of the finished parts in the press direction are ensured. In addition, relative movements in the pressure contact zone between workpiece and impression are reduced and thus the wear of the dies is reduced. By the use of preshaping methods preceding the die forging, the use of material can be reduced by up to a third.
In massive forming, a trend toward a higher and higher number of strokes has recently been detected. This is achieved in particular through the use of modern crank presses having fully automatic workpiece transfer for the die forging. The known preshaping methods, in particular transverse rolling and stretch rolling, have the disadvantage that they can only be integrated with difficulty in a fully automatic forging process with automatic workpiece transport. The reasons for this are the relatively high cycle times during the transverse or stretch rolling, and the partly unsuitable position of the workpiece at the end of the rolling operation for an automated production process.
A further disadvantage is the complicated design of the preshaping device and the associated high costs.